Liquid-like nanomaterials are emerging as unique nanolubricating materials due to their combined advantages of fluidity and nanoscale size. However, their development and application have been hindered by relatively complex synthesis processes. Herein, a one-step method for synthesizing liquid-like carbon dots (LCDs) was developed by introducing ammonium salts into a citric acid–based synthesis system. Compared to solid carbon dots (CDs) synthesized with citric acid, LCDs exhibit liquid-like characteristics, which were further explored through molecular simulations. When used as additives in lubricating grease, LCDs demonstrate excellent tribological performance, including friction reduction, antiwear properties, and improved load-carrying capacity. This study not only introduces a simple and cost-effective strategy for producing LCDs, advancing the development and application of CDs but also expands the understanding of CDs as additives in lubricating grease.